In a large non-stick skillet, melt the butter. Add the sugar so that it covers the bottom of the skillet. Cook over medium heat until the sugar melts and turns golden brown. Add the apples and stir with a wooden spoon until the McIntosh apples break apart and the Cortland apples become soft, about 10 minutes. Let cool completely while preparing the dough.
In a food processor, combine the flour, starches and salt. Add the butter and pulse a few seconds at a time until it forms pea-sized pieces. Add the egg and water. Pulse again until the dough just begins to form. Remove the dough from the processor and form into two discs with your hands. Cover with plastic wrap and refrigerate for 30 minutes.
With the rack in the lowest position, preheat the oven to 400°F (200°C).
Between two sheets of parchment paper, roll out one disc of dough to line a 9-inch (23 cm) in diameter, 1-inch (2.5 cm) deep tart pan with removable bottom. Keep the other disc of dough for another use. Fill the tart pan with the cooled apples. Set aside.
In a bowl, combine the oatmeal, brown sugar and ground almonds. Add the butter and mix with your fingertips until the ingredients are just moistened. Spread over the pie. Bake for 25 to 30 minutes or until the crumble is golden brown. Let cool on a wire rack.
There are three brands of pure (gluten-free) oatmeal available on the market: Château Cream Hill, Only Oats and Bob's Red Mill. If you can’t find one of those, you can also prepare the crumble with certified gluten-free quinoa flakes.
If you find the dough is too fragile after rolling out between two sheets of parchment paper, refrigerate it for a few minutes. The paper should easily peel off the dough and it will be easier to line the tart pan.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.